"It personally affected me a little bit because I had done an interview with Mr. McCormick about 10 minutes before we got the call, and we had talked a little bit about how he wanted us to stay safe and how we wanted him to stay safe," Tennant told reporters.

The ground was saturated from the rain, and a large tree about one metre in diameter fell on the journalists' SUV, apparently as it was driving along Highway 176, Tennant said. When first responders arrived, the engine was running and the transmission was in drive, Tennant said.

"It is a freak of nature," he said.

Tennant thinks the roots of the 91-centimetre-diameter tree were loosened in the ground saturated by a week's worth of rain.

The fringes of Alberto brought up to 50 millimetres of rain to the area on Monday.

The station, which broke the news on air, said the pair was heading to a story when they were killed.

Anchor Carol Goldsmith said McCormick and Smeltzer were "beloved members of our team - our family".

The accident happened not far from where a landslide killed a woman in her home on May 19 after heavy rains.

WYFF-TV is based in Greenville, South Carolina. The station said the pair had worked in the area for more than a decade.

Forecasters warned that downpours from the vast system of swirling storm bands now raise the danger of flash flooding across several southern states in coming days. Alberto's ragged core made landfall near Laguna Beach in the Florida Panhandle on Monday afternoon, local time, before it began crawling inland.

The National Hurricane Centre in Miami said Alberto was centred near the community of DeFuniak Springs in the Florida Panhandle at about 7pm on Monday. With maximum sustained winds of 65 kilometres per hour, it had begun weakening as it moved to the north at 17 km/h

As it heads inland it is being deprived of the warm waters that fuel tropical weather systems, causing it to weaken, forecasters said. A subtropical storm like this has a less defined and cooler centre than a tropical storm, and its strongest winds are found further from its centre.

AP